It is important in many types of seating, especially the types of seating used in commercial and professional operations such as by typists, computer operators, draftsman and the like that the position of the back be capable of accurate and precise adjustment. It is known that seating that does not provide effective, adequate and comfortable body support results in premature fatigue as well as physical discomfort. If the condition prevails over a long period of time, it may result in physical disabilities of one type or another on the part of the user.
While adjustable back mechanisms and supports have been known for a long time, these mechanisms have been subject to one or more of various types of shortcomings. Among the major of these shortcomings has been the fact that many mechanisms are subject to failure should the user suddenly lean backward, imposing a shock load on the hinge of the pivot joint about which the back is adjusted. Another shortcoming in the case of many of the known adjustable back supports is that they are capable of providing only a limited number of adjusted positions and, thus, are not necessarily capable of positioning the back in the most effective position for the particular operator or the particular operation which the operator is conducting while utilizing the seating.
In satisfying the requirements of both infinite adjustment and a structure which is dependable, it is important to consider that the pivot joint about which the back is made adjustable is subject to very heavy loads, even under normal operating conditions. It is also subject to severe shock loading as well as frequent abuse. It is thus important to provide a hinge or pivot joint which can sustain this type of usage over a long period of time. It must also be a joint which once locked in a particular position will retain this position under all normally expected operating conditions including those which impose severe forces tending to shift the back from its selected positions. It is important that the joint resist the tendency to crimp under repeated impact of a user sitting back in the seat.
Other desirable criteria is providing a pivoted back support for a chair and that it be compact and that it have a neat and attractive appearance.